1. Field of the Invention
The present invention relates to a region searcher, a method of driving the same, and a code searcher using the same, in particular, a region searcher which the complexity of the implementation thereof can be remarkably reduced by storing the energy value corresponding to the same hypothesis location value by using a searcher having divided two buffers, without simply using a memory, when a predetermined region is iteratively searched.
2. Description of the Prior Art
Generally, in the code division multiple access type cellular radio telephone communication system, the location of the spread code must be found. For this, there are a method using an active type correlator structure and a method using a passive type matched filter structure.
The method using the active type correlator structure is used in a terminal and so forth, because the structure thereof is simple. However, there is a problem that the signals must be collected for a long time in order to use the signal required for increasing the gain of a received signal. In addition, in this method, the used signal can not be repeatedly used, and the searching time thereof becomes longer than that of the method using the matched filter, because the signals arrived in the different time are collected and used as the location information of the spread code.
In the method using the matched filter structure, the received signals are stored in a buffer in received order and are multiplied by an expected input signal, thereby the sum of products is used as the location information of the spread code. Accordingly, since the location information of the spread code for every input signal sample is generated, the region can be searched at high speed. However, in order to obtain the needed signal gain, the length of the buffer must be long. Also, because the operation thereof is accomplished at the signal rate of the input sample, the structure thereof is complicated and the power consumption becomes increased.
FIG. 1 is a block diagram of a spread code searcher used in a conventional code division multiple access (CDMA) type cellular radio telephone communication system.
Referring to FIG. 1, the spread code searcher comprises a matched filter 10, an energy value converting section 11, an address generating section 12, a first memory section 13, and a second memory section 15.
The matched filter 10 receives in-phase signal (I data) and quadrature-phase signal (Q data), constructs the matched filter type structures using a predetermined spread signal pattern, and outputs the correlated values of the input signal. In this case, the correlated values are output to the energy value converting section 11 at every hypothesis location, and the energy value converting section 11 squares each of phase signals, and adds them to be converted to an energy value, such that each of the phase components in the in-phase signals and the quadrature-phase signals due to Rayleigh fading effect of the channel included in the correlated value is removed. Such obtained values exist in the hypothesis location in all.
In addition, if the signal-to-noise ratio thereof is very small, the obtained energy value therein is very small. Therefore, the energy values are iteratively obtained and are added them in order to increase the signal value. For performing such operation, the energy value obtained at the each of the hypothesis location is stored in the first memory section 13 so as to be added to a value that is newly obtained at the same hypothesis location. In case of constructing the structure by using the first memory section 13, an address for controlling the first memory section 13 must be generated in the address generating section. Also, the second memory section 15 for finding and storing the largest value among the values stored in the first memory section 13 is further needed.
In the code division multiple access type cellular radio telephone communication system, in order to find such a spread code location, a known signal having the inherent orthogonal characteristics is transmitted in case of a forward link which a base station transmits a signal to a terminal, and an inherent code signal using the high self-correlated property is transmitted in case of a reverse link which a terminal transmits a signal to a base station. Since these signals are used within the limited signal power in the overall system, the power of these signals cannot become larger than the certain limit.
In case where the location information of the spread code is obtained as mentioned above, when the power of the signal obtained at a time is not enough to determine the location, the signals are iteratively obtained at the searched region and are added to the previous obtained value, thereby the signal having the larger value can be obtained. At this time, if the size of the searched region is increased, in order to store the information therefor, a device for storing information having the value corresponding to the spread code location included in the searched region is needed.